1) Field of the Invention
The present invention relates to medical devices and, in particular, to a medical device for treating a target site within the body, such as a vascular abnormality, that includes multiple layers and one or more gaps between layers for more effectively treating the target site.
2) Description of Related Art
An aortic aneurysm is a weak area in the aorta, the main blood vessel that carries blood from the heart to the rest of the body. A common aneurysm is the abdominal aortic aneurysm (“AAA”), which may be caused by arteriosclerosis. As blood flows through the aorta, the weak vessel wall thins over time and expands like a balloon and can eventually burst if the vessel wall gets too thin. Most commonly, aortic aneurysms occur in the portion of the vessel below the renal artery origins. The aneurysm may be located in the vessels supplying the hips and pelvis, including the iliac arteries.
Rather than performing surgery to repair an aneurysm, vascular surgeons may install an endovascular stent graft delivered to the site of the aneurysm using elongated catheters. A stent graft can be used for a variety of conditions involving the blood vessels, but most commonly is used to exclude an aneurysm. The stent graft may be delivered to a location bridging the aneurysm, at which point the stent graft is deployed and expanded to approximately the normal diameter of the aorta at that location. Over time, the stent graft becomes endothelialized and the space between the outer wall of the stent graft and the aneurysm ultimately fills with clotted blood, which prevents the aneurysm from growing further since the stent graft bypasses (excludes) the aneurysm and prohibits systematic pressure and flow on the weakened segment of the lumen.
Depending on where the aneurysm is in relation to other branch vessels, different design variations may be needed. For example, in treating an AAA, the stent graft should be placed so as not to exclude blood flow through the renal arteries which branch off from the abdominal aorta. Moreover, the stent graft should be anchored within the lumen to reduce the incidence of migration, such as by promoting endothelialization or fixation with the lumen. Endoleaks may occur as a result of blood flowing around the stent, which may result in further weakening of the site of the aneurysm.
Medical devices, such as multi-layered occluders and stent grafts, have also been developed in order to occlude or exclude vascular abnormalities such as aneurysms. For example, the medical devices may include multiple layers of coaxially disposed layers of material that are configured to substantially slow the flow of blood and facilitate thrombosis. The idea is that having a greater surface area using a multi-layered device may speed clot formation in comparison to single layer devices and eliminate the need for an additional material such as a polyester fabric often included in single layer devices.
Despite these improvements in occluding vascular abnormalities, there is needed a multi-layer device that is capable of more effectively treating various target sites. Moreover, there is a need for a medical device that may be easily delivered and adequately anchored at the target site. In addition, there is a need for a medical device that may be delivered to a target site that is less traumatic to the vasculature and that may be used to prophylactically treat various conditions that may be in more difficult to reach anatomy. There is additionally a need for medical device that may promote thrombosis to occlude and/or exclude an aneurysm or other vascular abnormality.